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Mac full?
Picking an external drive

For anyone whose Mac is nearly full and is about to buy a drive
No. 157Inside Computers & the InternetPart 28 of 28Fact-checked Oct 9, 2026
Video2:19 · English voice (AI) · English subtitles

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The full narration of the video.

The box says two thousand per second. Plug it into a Mac, and you get just over one thousand. The extra money? Wasted. Your Mac is out of space and you want an external drive. So what should you look for? First, why external at all? On most Macs, the storage is soldered to the board. Once you buy it, you can't add more.

Think of your Mac as your home. The built-in drive is the closet: handy, but pricey. An external drive is a storage unit downstairs. One: what goes downstairs? Apps you use every day stay home. Photos, videos, finished projects: bulky and rarely opened. Move them down. Two: which kind of storage unit? One kind has a spinning platter inside, like a record player. Cheap and roomy, but slow, and it hates being dropped.

The other is all chips, no moving parts. About ten times faster. And bumps don't bother it. If you grab things from it every day, go with chips. For backups you plug in now and then, a spinning one is fine. Three, the easiest place to slip up: how wide is the road? Everything travels through a port on your Mac. Then through a cable. If the road is narrow, a fast box doesn't help.

Take an ordinary external drive and plug it into a Mac. The port tops out around one thousand per second. So the ones labeled two thousand can't run flat out on a Mac. Don't pay extra for that. For real speed, get one marked Thunderbolt. It can go past two thousand. Same with the cable. Apple's charging cable moves data twenty times slower. Use the cable that came with the drive.

Four: change the lock to a Mac lock. When a new drive arrives: wipe it first with Disk Utility, which comes with your Mac. Mac only? Choose the one called APFS. Also using it with a Windows PC? Choose exFAT. Wiping erases everything, so copy anything on it off first. Five: how big? For the drive that backs up your Mac automatically: Apple suggests at least twice your Mac's storage.

One more thing people miss: once you move it down, the copy in storage is the only copy. If that drive dies, it's all gone. Keep a second copy of the photos that matter. Now open System Settings, then General, then Storage: see what's taking up the most room. Come back and tell me what's the biggest thing in your closet.

1

Says 2000,
runs at 1000

2000 1000

Speed isn’t just about the box. It’s also the port on your Mac and the cable in between. If the road is narrow, a fast box doesn’t help.

Before you buy, settle these five things.

2

The closet at home,
the storage unit downstairs

On most Macs the storage is soldered to the board. Once you buy it, you can’t add more. The only way to get more room is to plug a drive in.

The built-in drive is the closet at home: handy, but pricey. An external drive is a storage unit you rent downstairs.

Storage isn’t memory: they do different jobs. See this episode.

3

One:
what goes downstairs

MOVE OUT
Photos, videos, finished projects
Bulky, and you rarely open them
KEEP HOME
The system and everyday apps
You need them daily; unplug the drive and they won’t open

Moving your Photos library has three rules: the drive must use a Mac format (see Four), it can’t be your Time Machine backup drive, and it must be plugged in when you open Photos.

4

Two:
spinning disk or chips

SPINNING
Cheap and roomy, but slow and fragile
Portable ones move about 120 per second
CHIPS
About ten times faster, shrugs off bumps
Sold as “SSD” or “solid state”

Grab files from it every day? Get chips. Just backups, plugged in now and then? A spinning one is fine.

5

Three:
how wide is the road

Files travel through a port on your Mac, then through a cable. The narrowest part sets the speed (rough megabytes per second below).

Charge cable 50
USB port 1000
Thunderbolt 2500+

A regular USB drive on a Mac tops out around 1000 per second. Drives rated 2000 (labeled “USB 3.2 Gen 2×2”) can’t run flat out on a Mac, so don’t pay extra for them.

Thunderbolt Want real speed? Get a drive marked Thunderbolt. On a Mac it can reach 2,500–3,000.

Same with cables: Apple’s charge cable moves data at about a twentieth of that speed. Use the cable that came with the drive. Some Macs have two ports that differ (the MacBook Neo’s right port is slower), so use the left.

6

Four:
switch to a Mac lock

MAC ONLY
Pick APFS
Apple’s own format, best for SSDs
ALSO WINDOWS
Pick exFAT
Both sides can read and write

When a new drive arrives, erase it once in Disk Utility, which comes with your Mac. That changes the lock. Erasing wipes everything, so copy off anything on it first.

7

Five:
how big

Mac Backup

For your automatic backup drive, Apple suggests at least twice your Mac’s storage.

A 512GB Mac means a backup drive of 1TB or more. For the photo and video drive, double what you have now and it will last years.

8

Once you move it,
it’s the only copy

If this drive dies,
it’s all gone
After you delete it from your Mac, the copy in storage is the only one. Keep a second copy of photos that matter, on a backup drive or in the cloud.
Open Storage
and find the biggest item.
It’s in System Settings › General.
Come back and tell me: what’s the biggest thing in your closet?
Made by Samshang × Maddox
Sources: Apple Support, “Move your Photos library to save space on your Mac” (108345: APFS or Mac OS Extended, not on a Time Machine drive, must stay connected); Apple Support, “About the Apple Thunderbolt 3 (USB-C) Cable” (111750: USB-C Charge Cable data limited to 480Mbps); Apple Mac User Guide, “Time Machine recommends a larger backup disk” (at least twice); Apple MacBook Neo User Guide, “USB-C ports” (left USB 3, right USB 2); Eclectic Light Company (2024-12-25) on Apple silicon Macs lacking USB 3.2 Gen 2×2 and capping at 10Gb/s; Kingston, “HDD vs External SSD,” and DiskGenius (portable hard drives about 120MB/s, NVMe SSDs 1000MB/s+); Thunderbolt SSDs at about 2500–3000MB/s on a Mac are approximate review figures; AppleInsider (2026-03-03) on Mac storage being chosen only at purchase.
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